Bodies are repelled from the Pules of a Magnet. 279 



quer ces mouvements clu bismuth cristallise, comnie on a essaye 

 de la faire, par la force repulsive de I'aimant, qui, suivant I'expe- 

 i-ience de M. Tyndall*, s'exerce avec plus d'intensite parallele- 

 ment aux clivages que dans la direction perpendiculaire a ces 

 plans. 



"Remarquons encore qu'on ne trouve pas constamment Taccord 

 qui devrait exister, selon les idees de MM. Tyndall et Knoblauch, 

 entre les phenomenes magneto-cristallises et les effets produits 

 par la compression dans le bismuth, si Pon considere ces plans 

 de clivages et la ligne suivant laquelle la compression a eu lieu 

 comme jouissant des memc proprietesf." 



With regard to the first objection, I may say that it is ex- 

 tremely difficult to meet one so put ; it is simply an opinion, and 

 I can scarcely say more than that mine does not coincide with 

 it. I would gladly enter upon the subject and endeavour to 

 give the objection a scientific form were the necessary time at 

 my disposal, but this, I regret to say, is not the case at present. 

 I shall moreover be better pleased to deal with the objection 

 after it has assumed a more definite form in the hands of its 

 proposer, for I entertain no doubt that it is capable of a sufficient 

 answer. The second objection M. [Matteucci considers to be a 

 more grave one. The facts are as follows : — the repulsion of a 

 mass of crystallized bismuth depends upon the direction in which 

 the mass is magnetized. When the magnetizing force acts in a 

 certain direction, the intensity of magnetization, and the conse- 

 quent repulsion of the mass, is a maximum. This is proved by 

 placing the mass upon the end of a torsion beam and bringing 

 its several directions successively into the line of the magnetic 

 force. Poisson would have called such a direction through the 

 mass a principal axis of magnetic induction, and I have else- 

 where called it a line of elective polarity. When a sphere or 

 cube of bismuth is freely suspended in the magnetic field, with 

 the direction referred to horizontal, in all positions except two 

 the forces acting on the mass tend to turn it ; those positions 

 are, when the hue of maximum magnetization is axial and when 

 it is efjuatorial, the former being a position of unstable, and the 

 latter a position of stable equilibrium. When the above line is 

 oblique to the direction of magnetization, the sphere or cube will 

 turn round its axis of suspension until the direction referred to 

 has set itself at right angles to the line joining the poles. Now 

 if the direction of maximum magnetization be transverse to an 

 elongated mass of bismuth, such a mass must, when the said 

 direction recedes to the equator, set its length from pole to pole. 



* This was first proved by Mr. Faraday.— J. T. 

 t Cours special sur V induction, Sfc, p. 255. 



